Building a Store Application With MySQL++ and C/C++ - A basic program

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Before we begin this section, you will need to download MySQL++, which is the C++ library for interacting with MySQL databases. You can download it here and it's around 700KB. Just like MySQL, MySQL++ works on a verity of different platforms and compilers. Consult the documentation accompanying the download for the necessary information regarding your compiler. I personally use Borland's C++ Builder 5.0, but I've also worked with MySQL on Microsoft's Visual C++ 6.0, which is what I will be using throughout this article.

Once you've downloaded MySQL++, it's extremely easy to include MySQL support into your applications. Extract the zip file to c:\mysql++. Copy c:\mysql++\mysql\lib\libmySQL.dll to c:\winnt\system32 and create a new console application in Visual C++. Click the Project -> Settings menu and go to the C/C++ tab. Choose the preprocessor category and add the following line to the additional include directories text box:

c:\mysql++\include,c:\mysql++\mysql\include

Click OK. Lastly, right click on the resource files node and add c:\mysql++\lib\mysql++.lib. If you're not using Visual C++ then consult the documentation that comes with your version of MySQL++. With that said, we can begin writing a very basic program to interact with our database. Our program will connect to and then disconnect from the database.

Firstly, we need to include some header files:

#include <stdio.h>

#include <mysql++.h>

Next we will create a pointer to the MySQL structure that will hold our connection. This structure is defined in the MySQL header file. What it basically does is represent a handle to a database connection. If you would like to connect to more than one database in your application then you will need to declare more than one MYSQL structure.

MYSQL *pConnection;

To initialize our MYSQL structure we must call mysql_init(). It will allocate the required memory, initialize and then return a pointer to a MYSQL object:

pConnection = mysql_init(NULL);

To be on the safe side, you might want to check that a pointer to a MYSQL object is actually returned. You can do this by checking if pConnection is null or not. Next, we actually connect to the database using mysql_real_connect(). Here's the declaration of mysql_real_connect():

mysql_real_connect MYSQL *mysql, const char *host, const char *user, const char *passwd, const char *db, unsigned int port, const char *unix_socket, unsigned int client_flag)

As you can see, there's quite a lot of parameters that the mysql_read_connect function accepts. Here's a brief breakdown of what each parameters represent:

• mysql: The first parameter is the MYSQL structure we've created above. It will hold the information concerning the connection once we connect to MySQL.
• host: The second parameter is the location of the database server. If the database is installed on your computer locally, then you would use "localhost".
• user/passwd: The third and fourth parameters are the username and password of a valid MySQL user account.
• db: The fifth parameter is the database you would like to connect to. In our case this will be "Article1".
• port: The sixth parameter is the port your database server will listen on. Pass 0 to indicate that the default MySQL port should be used.
• unix_socket: The seventh parameter is the Unix socket number. We will pass NULL to indicate that we don't require a special Unix socket.
• client_flag: The last parameter is reserved for certain flags we may want to use, for example passing CLIENT_SSL will use the SSL encryption protocol or CLIENT_COMPRESS will use a compression protocol. For a full list of flags and their descriptions, consult the MySQL++ documentation. We will pass a 0, as we do not require any of the flags.

Here's how our function call will look (note that the function will return a NULL value on an unsuccessful connection attempt):

mysql_real_connect(pConnection, "localhost", "admin", "password", "Article1", 0, NULL, 0);z

Before we take our application to the next level, you have to know one last thing which is how to disconnect from the database. This is accomplished by a simple call to mysql_close(). The functionrequires a pointer to a MYSQL object as its only parameter. Mysql_close() will close the connection and free the memory allocated to the MYSQL structure:

mysql_close(pConnection);

Putting everything together, here's our first C++ application that uses MySQL++ to connect to and disconnect from our MySQL database, Article1:

#include <stdio.h>

#include <mysql++.h>

MYSQL *pConnection;

int main(int argc, char* argv[])

{

pConnection = mysql_init(NULL);

if(!pConnection) //error, quit the program

return 0;



printf("Attempting to connect\n");



if(mysql_real_connect(pConnection,"localhost","admin","password","Article1",0,NULL,0) == NULL) //error, quit the program

return 0;



printf("Connected to the database\n");

mysql_close(pConnection);

printf("Connection Terminated\n");



return 0;

}

Next: Bringing it all together >>
 

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